1. Field of the Invention
The present invention relates to an image display apparatus having a function to correct trapezoidal distortion caused when a screen image is projected on a screen from an angle, an information processing apparatus having the image display apparatus, and a method of controlling the image display apparatus.
2. Description of Related Art
An image display apparatus that projects a screen image on a screen has no problem if the screen image is projected on the screen straight from a side of the apparatus. In the case where the screen image is projected on the screen from an angle, however, what is commonly called trapezoidal distortion occurs, in which an rectangular output screen image is distorted into a trapezoidal shape. Then, trapezoidal distortion correction (Keystone correction) is performed to convert the rectangular output screen image into a trapezoidal shape in the reverse direction of the distorted trapezoidal shape of the screen image projected on the screen. Thus, a non-distorted rectangular screen image can be displayed on the screen.
Such trapezoidal distortion correction may be configured such that a user manually makes an adjustment while viewing the screen image on the screen. As described in Japanese Patent Application Publication No. 1997-270979 or No. 2006-14233, for example, due to cumbersomeness in adjustment, a technology is known that automatically corrects trapezoidal distortion, thus eliminating manual adjustment by a user. Such a technology detects with a sensor an installation angle at which an image display apparatus itself is installed in a tilted state and corrects trapezoidal distortion in accordance with the installation angle.
In the conventional technology, the image display apparatus itself is installed in a tilted state. As shown in FIGS. 16A and 16B, however, a projection unit 112 of an image display apparatus 111 is rotatably provided in a main body 113 so as to substantially change a projection angle. Then, a screen image can be projected on a wall 114 as a screen as shown in FIG. 16A and on a ceiling 115 as a screen as shown in FIG. 16B, thus enhancing usability.
The conventional technology corrects trapezoidal distortion based on a case where a screen image is projected obliquely upward, similar to the case shown in FIG. 16A. As shown in 17, a correction factor is set to be greater as the projection angle increases. The projection angle θ is a tilt angle of an optical axis of projected light relative to the horizontal direction. The correction factor represents a ratio of an upper edge and a lower edge of a screen image displayed in a trapezoidal shape on the screen.
In the case of projection upward to the wall shown in FIG. 16A, the distance to the wall 114 is greater on the upper edge of the screen image. When a rectangular output screen image shown in FIG. 18A-1 is projected on the wall 114, the screen image projected on the wall 114 has a trapezoidal shape having the upper edge greater than the lower edge as shown in 18B-1. In correction of trapezoidal distortion using the correction factor shown in FIG. 17, the upper edge portion of the screen image is compressed as shown in FIG. 18C-1, and thereby the screen image on the wall 114 is displayed in a non-distorted rectangular shape having the upper edge and the lower edge in the same length as shown in FIG. 18D-1.
In the case of projection on the ceiling shown in FIG. 16B, meanwhile, the distance to the ceiling 115 is greater on the lower edge of the screen image. When a rectangular output screen image shown in FIG. 18A-2 is projected on the ceiling 115, the screen image projected on the ceiling 115 has a trapezoidal shape having the lower edge greater than the upper edge as shown in 18B-2, opposite to the case of projection upward to the wall. In correction of trapezoidal distortion similar to the case of projection upward to the wall, the upper edge portion of the screen image is compressed as shown in FIG. 18C-2. Since the correction expands the distortion of the projected screen image, the screen image projected on the ceiling 115 is substantially distorted as shown in FIG. 18D-2, substantially falling short of the concept of automated screen image adjustment.